Automated vehicle radar system with auto-alignment for azimuth, elevation, and vehicle speed-scaling-error

ABSTRACT

In accordance with one embodiment, a radar system with auto-alignment suitable for use in an automated vehicle is provided. The system includes a radar-sensor, a speed-sensor, and a controller. The radar-sensor is used to detect objects present in a field-of-view proximate to a host-vehicle on which the radar-sensor is mounted. The radar-sensor is operable to determine a measured-range-rate (dRm), a measured-azimuth-angle (Am), and a measured-elevation-angle (Em) to each of at least three objects present in the field-of-view. The speed-sensor is used to determine a measured-speed (Sm) of the host-vehicle. The controller is in communication with the radar-sensor and the speed-sensor. The controller is configured to simultaneously determine a speed-scaling-error (Bs) of the measured-speed, an azimuth-misalignment (Ba) of the radar-sensor, and an elevation-misalignment (Be) of the radar-sensor based on the measured-range-rate, the measured-azimuth-angle, and the measured-elevation-angle to each of the at least three objects, while the host-vehicle is moving.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to a radar system, and moreparticularly relates to a system that auto-aligns a radar-sensor whilethe host-vehicle of the system is moving.

BACKGROUND OF INVENTION

It is known that automotive radar-sensors need to be aligned with thechassis of a host-vehicle so the location of detected objects isaccurately known. Alignment procedures performed when the host-vehicleis assembled are not able to compensate for pitch or elevation errorscaused by heavy cargo and yaw or azimuth errors caused by miss-alignmentof the wheels or chassis of the host-vehicle which may cause ‘crabbing’or ‘dog-tracking’ by the host-vehicle while traveling.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a radar system with auto-alignmentsuitable for use in an automated vehicle is provided. The systemincludes a radar-sensor, a speed-sensor, and a controller. Theradar-sensor is used to detect objects present in a field-of-viewproximate to a host-vehicle on which the radar-sensor is mounted. Theradar-sensor is operable to determine a measured-range-rate (dRm), ameasured-azimuth-angle (Am), and a measured-elevation-angle (Em) to eachof at least three objects present in the field-of-view. The speed-sensoris used to determine a measured-speed (Sm) of the host-vehicle. Thecontroller is in communication with the radar-sensor and thespeed-sensor. The controller is configured to simultaneously determine aspeed-scaling-error (Bs) of the measured-speed, an azimuth-misalignment(Ba) of the radar-sensor, and an elevation-misalignment (Be) of theradar-sensor based on the measured-range-rate, themeasured-azimuth-angle, and the measured-elevation-angle to each of theat least three objects, while the host-vehicle is moving.

Further features and advantages will appear more clearly on a reading ofthe following detailed description of the preferred embodiment, which isgiven by way of non-limiting example only and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is diagram of a radar system with auto-alignment in accordancewith one embodiment;

FIG. 2 is a traffic scenario that may be encountered by the system ofFIG. 1 in accordance with one embodiment;

FIG. 3 is a diagram of an algorithm executed by the system of FIG. 1 inaccordance with one embodiment;

FIG. 4 is a graph of performance results of the system of FIG. 1 inaccordance with one embodiment;

FIG. 5 is a graph of performance results of the system of FIG. 1 inaccordance with one embodiment;

FIG. 6 is a graph of performance results of the system of FIG. 1 inaccordance with one embodiment;

FIG. 7 is a graph of performance results of the system of FIG. 1 inaccordance with one embodiment; and

FIG. 8 is a graph of performance results of the system of FIG. 1 inaccordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a non-limiting example of a radar system 10,hereafter referred to as the system 10. The system 10 is generallysuitable for use in an automated vehicle, a host-vehicle 12 for example,and is equipped with an auto-alignment feature for aligning aradar-sensor 14 with a reference frame established by the body of thehost-vehicle 12. The performance and utility of an automotive radarsystem is improved if the radar target tracker algorithm, hereafterreferred to as the tracker, has knowledge of (i.e. is programmed orcalibrated with) the actual angular mounting orientation of theradar-sensor relative to the field-of-view 16 observed by theradar-sensor and/or the vehicle or structure on which the radar-sensoris mounted. Advantageously, this is accomplished using an auto-alignmentalgorithm, hereafter often referred to as the algorithm 18, whichdetermines an actual or true angular orientation the radar-sensor(s).

The actual angular orientation is usually a small deviation from anexpected or typical orientation that the tracker has been preprogrammedwith. The auto-alignment algorithm described herein is for use on ahost-vehicle as it observes or tracks stationary objects or targets asthe host-vehicle travels along a road. It has been observed that theauto-alignment algorithm described herein is an improvement over priorexamples of auto-alignment algorithms as the prior examples take severalminutes or more to complete the auto-alignment process, require astationary host-vehicle with a pre-determined arrangement of referencetargets, and/or are prone to error as the correction factors needed tocompensate for the small deviation from the expected or typicalorientation are determined sequentially as the vehicle travels which canintroduce unknown errors.

Some known radar systems used on vehicles only perform an azimuth angleauto-alignment as those systems are only capable of detecting range andazimuth angle to a target or object. The radar system described hereinis further able to measure elevation angle in addition to range andazimuth angle, so an elevation alignment is also desired.

An auto-alignment method has been proposed that compares a detectedrange-rate of a stationary target to a measured speed of thehost-vehicle, and compensates for azimuth angle to the stationarytarget. However, the speed generally has a ‘speed ratio’ orspeed-scaling-error, meaning that the measured speed is proportional tothe actual speed with an error of a certain percentage, 1% for example.This proportionality error can be due to, for example, worn tire rubber,and/or wheels with non-standard radii. Depending on how theauto-alignment algorithm is configured, the effect of thespeed-scaling-error on estimated misalignment angles can be significant.

The auto-alignment algorithm described herein jointly or simultaneouslyestimates the speed-scaling-error, azimuth alignment error(azimuth-misalignment), and elevation alignment error(elevation-misalignment). Simultaneous computation is advantageous asmutual correlations of the errors are considered. That is, the algorithmdescribed herein is superior to the algorithms that compute these errorsseparately, e.g., computing one error after another. Separate orsequential computation suffers from the mutual correlation of the errorsbecause, for example, the azimuth-misalignment depends on the other twoerrors. In order to minimize the inaccuracies, multiple iterations maynecessary which undesirably takes time.

It acknowledged that it is known to perform a static calibration thatmeasures the radar-sensor mounting angles using a stationaryhost-vehicle and a known set of reference targets, e.g.—cornerreflectors located at carefully measured positions in an open spacearound the vehicle. However, this technique is deemed inadequate becausethe host vehicle's dynamic longitudinal axis is not easily determinedfrom visual inspection of a stationary vehicle. For example, the vehiclemight ‘crab’ as it moves in a straight line down the road, meaning thatwhat appears to be the longitudinal axis of the host-vehicle determinedbased on visual symmetry of the vehicle body might actually be pointingin a substantially different direction when the vehicle is moving. Assuch, azimuth angle misalignment will occur regardless of how carefullythe test measurements were taken. Also, changes in cargo load can affectthe elevation angle of the radar-sensor, which may be different fromwhen the static calibration was performed.

Continuing to refer to FIG. 1, the radar-sensor 14 is used to detectinstance of objects 20 present in a field-of-view 16 proximate to thehost-vehicle 12 on which the radar-sensor 14 is mounted. Theradar-sensor 14 is operable to determine or measure various values orvariable from the returned radar-signal reflected by the objects 20including, but not limited to, a measured-range-rate 22 (dRm), ameasured-azimuth-angle 24 (Am), and a measured-elevation-angle 26 (Em)to the objects 20. As will be described in more detail below, thealgorithm 18 needs at least three (3) instances of the objects 20 toperform the auto-alignment, so each of at least three (3) instances ofthe objects 20 must be present in the field-of-view 16.

FIG. 2 illustrates a non-limiting example of a traffic-scenario 28 thatmay be experienced by the host-vehicle 12 while the system 10 attemptsto auto-align the radar sensor 14. As will also be described below, theauto-alignment process carried out by the algorithm 18 is greatlysimplified when each of the at least three objects is not moving, i.e.can be characterized as stationary. By way of example and notlimitation, the objects 20 used as points of reference by the system 10for auto-alignment may include a stop-sign 20A, a speed-limit-sign 20B,and/or a stopped-vehicle 20C. By way of further example, anapproaching-vehicle 20D would not be a preferable instance of theobjects 20 to use for auto-alignment unless the speed of theapproaching-vehicle 20D was known by the system 10 because theapproaching speed was communicated to the system 10 by way ofvehicle-to-vehicle (V2V) communications, the configuration and operationof which is recognized by those in the art.

The system 10 also includes a speed-sensor 30 used to indicate ordetermine a measured-speed 32 (Sm) of the host-vehicle 12. By way ofexample and not limitation, the speed-sensor 30 may be the same sensorused to determine what speed to indicate on a speedometer display (notshown) of the host-vehicle 12, which would be based on the rotationalspeed of the wheels of the host-vehicle as will be recognized by thosein the art.

The system 10 also includes a controller 34 in communication with theradar-sensor 14 and the speed-sensor 30. The controller 34 may include aprocessor (not specifically shown) such as a microprocessor or othercontrol circuitry such as analog and/or digital control circuitryincluding an application specific integrated circuit (ASIC) forprocessing data as should be evident to those in the art. The controller34 may include memory (not specifically shown), including non-volatilememory, such as electrically erasable programmable read-only memory(EEPROM) for storing one or more routines, thresholds, and captureddata. The one or more routines may be executed by the processor toperform steps for determining error correction factors or offsets toauto-align the radar-sensor 14 based on signals received by thecontroller 34 as described herein.

As part of the auto-alignment process, the controller 34 is programmedwith the algorithm 18, so the controller 34 is configured to jointly orsimultaneously determine a speed-scaling-error 36 (Bs) of themeasured-speed 32, an azimuth-misalignment 38 (Ba) of the radar-sensor14, and an elevation-misalignment 40 (Be) of the radar-sensor 14 basedon the measured-range-rate 22, the measured-azimuth-angle 24, and themeasured-elevation-angle 26 to each of the at least three instances ofthe objects 20. Advantageously, the algorithm 18 performs theauto-alignment of the radar-sensor 14 while the host-vehicle 12 ismoving. It is noted that the algorithm 18 described herein isadvantageous over alignment schemes that would only align theradar-sensor 14 when the host vehicle is stopped and/or when presentedan arrangement of targets pre-positioned an known locations because thealgorithm 18 is able to correct for dynamic conditions of thehost-vehicle 12 such as wheel misalignment that affect het azimuthangle, and/or varying cargo loads that affect the elevation angle of theradar-sensor 14

The controller 34 may be further programmed or further configured todetermine an actual-speed 42 (Sa) based on the measured-speed 32 and thespeed-scaling-error 36, an actual-azimuth-angle 44 (Aa) to the objects20 based on the azimuth-misalignment 38 and the measured-azimuth-angle24, and an actual-elevation-angle 46 (Ea) to the objects 20 based on theelevation-misalignment 40 and the measured-elevation-angle 26. Thedetails of these calculations will also be presented below.

The algorithm 18 may collect a sufficient number of detections of theobjects 20 in a single instant, or may collect detections over amultitude of time instants. At some time instants, it may be that nosuitable detections are found, and these time instants can be ignored.By collecting data over many time instants, the corrupting effects oferrors not included in the model of algorithm are ‘averaged out’. Thedata from these multiple time instants can be batch processed, or arecursive filter can be used. In either case, the equation shown belowforms the heart of the implementation, and a person skilled in the artcould successfully implement either the batch or recursive forms of themethod.

The radar-sensor 14 described herein is assumed to be, without loss ofgenerality, mounted on the host-vehicle 12. A three-dimensional (3D)orthogonal Cartesian coordinate system is used, with origin ofcoordinates located at the radar-sensor 14. The positive x-axis pointshorizontally forward parallel to the vehicle's dynamic longitudinalaxis. The positive y-axis points in a horizontal lateral directiontoward the vehicle's right side. The positive z-axis points downward andis orthogonal to the x- and y-axes.

The actual-azimuth-angle 44 of the boresight vector of the radar-sensor14 is defined as the angle through which a vertical plane containing thepositive x-axis needs to be rotated about the z-axis (using a signconvention defined by the right-hand rule) in order to contain thedetection or boresight vector in that rotated vertical plane. Theactual-elevation-angle 46 (Ea) of the boresight vector of theradar-sensor 14 is defined as the angle through which a vector containedin the intersection of the x-y plane and the azimuthally-rotatedvertical plane needs to be rotated upward to be coincident with thedetection or boresight vector. Detections which are above the x-y planehave a positive elevation angle. This convention agrees with aright-hand rule about the y-axis.

Singularities in this representation of azimuth and elevation angles(e.g., at points on the z-axis) are not of concern in the automotiveapplication with radars having a somewhat limited verticalfield-of-view.

Definitions of the ‘actual’ (i.e. the measurement-error-free value)variable names or symbols, and the ‘measured’ (i.e. indicated bymeasurements made by the radar-sensor 14) variable names or symbols usedherein are defined as follows:

-   -   dRa(i), dRm(i): actual-range-rate 48 and measured-range-rate 22        of the i-th object detection;    -   Aa(i), Am(i): actual-azimuth-angle 44 and measured-azimuth-angle        24 of the i-th detection;    -   Ea(i), Em(i): actual-elevation-angle 46 and        measured-elevation-angle 26 of the i-th detection;    -   Ua(i), Va(i), Wa(i): actual-longitudinal, actual-lateral, and        actual-vertical components of the actual velocity vector or the        radar-sensor 14 relative to Earth at the time the i-th detection        is observed;    -   Um(i), Vm(i), Wm(i): measured-longitudinal, measured-lateral,        and measured-vertical components of measured velocity vector of        the radar-sensor 14 relative to Earth at the time the i-th        detection is observed;    -   Ut(i), Vt(i), Wt(i): longitudinal, lateral, vertical of        indicated velocity vectors relative to Earth of the i-the object        (i.e. target) detection;    -   Ys(i): side-slip-angle 50 of the host-vehicle 12 at the time the        i-th object detection is observed, where the slide-slip-angle is        the angle between the horizontal host-vehicle velocity vector        (i.e. the vector [Ua Va 0]) and the x-axis;    -   Ba: bias error in measured azimuth angle, i.e. the        azimuth-misalignment 38;    -   Be: bias error in measured elevation angle, i.e. the        elevation-misalignment 40; and    -   Bs: speed-scaling-error 36 in host vehicle speed.

The error models considered here can be summarized as:

Am(i)=Aa(i)+Ba: model of azimuth-misalignment  Eq. 1;

Em(i)=Ea(i)+Be: model of elevation-misalignment  Eq. 2;

and

Sm(i)=(1+Bs)*Sa(i): model of speed-scaling-error at the time the i-thdetection is observed  Eq. 3.

In the models of the azimuth misalignment and elevation misalignmentshown above, the misalignment is represented as a constant bias error inthe measured angle. In the speed scaling error model, the measured speedis modeled as the actual speed corrupted by the speed-scaling-error 36.The (1+Bs) form of the scaling-factor is useful because a value of Bs=0corresponds to zero measurement error.

The actual-range-rate 48 depends on the relative-to-Earth velocityvectors of the radar-sensor 14 and the instances of the objects 20 thatare detected, along with the actual-azimuth-angle 44 and theactual-elevation-angle 46 of the object detected relative to theradar-sensor 14. For the i-th detection, Eq. 4 defines theactual-range-rate 48 as—

dRa(i)=(Ut(i)−Ua(i))*cos [Aa(i)]*cos [Ea(i)]+(Vt(i)−Va(i))*sin[Aa(i)]*cos [Ea(i)]−(Wt(i)−Wa(i))*sin [Ea(i)]  Eq. 4.

Since the objects 20 (i.e. targets of interest) are intended or believedto be stationary, the values of Ut(i), Vt(i), and Wt(i) for all valuesof (i) are assumed to be identically equal to zero. Applying the errormodels defined above produces the equation below which can beimplemented in either batch or recursive form over multiple timeinstants with multiple radar detections as indicated in the precedingtext. As noted above, relative motion between the radar-sensor 14 andstationary targets (the objects 20) is necessary, hence theactual-longitudinal-speed of the radar-sensor, Ua(i), is assumed to benonzero. Combining Eqs. 1-4 produces Eq. 5, from which the errors Bs,Ba, and Be can be determined using:

dRm(i)+Um(i)*cos [Am(i)]*cos [Em(i)]+Vm(i)*sin [Am(i)]*cos[Em(i)]=[H(i,1)H(i,2)H(i,3)]*trans[Bs Ba Be]  Eq. 5,

where

H(i,1)=Um(i)*cos [Am(i)]*cos [Em(i)]  Eq. 6,

H(i,2)=−Um(i)*sin [Am(i)]*cos [Em(i)]+Vm(i)*cos [Am(i)]*cos[Em(i)]  Eq.7,

H(i,3)=−Um(i)*cos [Am(i)]*sin [Em(i)]−Vm(i)*sin [Am(i)]*sin [Em(i)]  Eq.8,

and

trans[ ] is the matrix transpose operation  Eq. 9.

In the derivation of Eq. 5 the measured value of the radar-sensor'slongitudinal and lateral velocities, Um(i) and Vm(i), are assumed to besubject to the same speed-scaling-error as Sm(i), that isUm(i)=(1+Bs)*Ua(i) and Vm(i)=(1+Bs)*Va(i), and the actual and themeasured vertical velocity of the radar-sensor, Wa(i) and Wm(i), areassumed to be zero.

Eq. 10 is a simplified version of Eq. 5 that is suitable for conditionsof operation in which the host vehicle is traveling in a straight line,i.e. the actual lateral velocity of the sensor is approximately zero.Eq. 10 is derived from Eq. 5 by setting Vm(i) equal to zero and dividingthough by Um(i), so

dRm(i)/Um(i)+cos [Am(i)]*cos [Em(i)]=[F(i,1)F(i,2)F(i,3)]*trans[Bs BaBe]  Eq. 10,

where

F(i,1)=cos [Am(i)]*cos [Em(i)]  Eq. 11,

F(i,2)=−sin [Am(i)]*cos [Em(i)]  Eq. 12,

and

F(i,3)=−cos [Am(i)]*sin [Em(i)]  Eq. 13.

To solve Eq. 5, the following signals or values are needed: A) Radarmeasurements dRm(i), Am(i) and Em(i), which are provided byradar-sensor, and B) Host velocity components Um(i) and Vm(i), recallthat Wm(i)=0 is assumed. The host module may measure the host speed Smdirectly, but may not be capable to measure the side-slip-angle 50 (Ys)directly. The side-slip-angle 50 can be computed based on combinationsof other variables such as the measured-speed 32, a yaw-rate-sensor 52,steering-angle-sensor 54, etc. Accordingly, the system 10 may includethe yaw-rate-sensor 52 which is used to determine a yaw-rate 56 of thehost-vehicle 12. Accordingly, the controller 34 is further configured todetermine the side-slip-angle 50 (Ys) of the host-vehicle 12 based onthe yaw-rate 56, and further determine the speed-scaling-error 36, theazimuth-misalignment 38, and the elevation-misalignment 40 based on theside-slip-angle 50. Many methods exist for this purpose, as will berecognized by those in the art. Regardless of which method is usedthere, the algorithm receives from the host module output values for Smand Ys. The measured host velocity components needed in Eq. 5 arecomputed using Um=Sm*cos [Ys], and Vm=Sm*sin [Ys]. If the host is or isalmost traveling straight on a flat road, then Ys is negligible. So thevelocity components are determined as Um(i)=Sm(i), and Vm(i)=0. Anon-limiting example of a diagram 58 of the algorithm is shown in FIG.3.

A batch least squares problem can be formed by stacking a number of Eq.5 or Eq. 10 vertically to form an array with one equation for each i-thdetection. Accordingly, for the i-th detection, Um(i), Vm(i), Wm(i),dRm(i), Am(i), Em(i) are collected for a total of N detections, where Nis greater than or equal to three (N≧3). For Eq. 5, a least squaresproblem leading to a batch solution could take the form:

$\begin{matrix}{{{D\; 1} = {H*P}},{where}} & {{Eq}.\mspace{14mu} 13} \\{{{D\; 1} = \begin{bmatrix}\begin{matrix}{{{dRm}(1)} + {{{Um}(1)}*{\cos \left\lbrack {{Am}(1)} \right\rbrack}*{\cos \left\lbrack {{Em}(1)} \right\rbrack}} +} \\{{Vm}(1)*{\sin \left\lbrack {{Am}(1)} \right\rbrack}*{\cos \left\lbrack {{Em}(1)} \right\rbrack}}\end{matrix} \\\vdots \\\begin{matrix}{{{dRm}(N)} + {{{Um}(N)}*{\cos \left\lbrack {{Am}(N)} \right\rbrack}*{\cos \left\lbrack {{Em}(N)} \right\rbrack}} +} \\{{Vm}(N)*{\sin \left\lbrack {{Am}(N)} \right\rbrack}*{\cos \left\lbrack {{Em}(N)} \right\rbrack}}\end{matrix}\end{bmatrix}},} & {{Eq}.\mspace{14mu} 14} \\{{H = \begin{bmatrix}{H\left( {1,1} \right)} & {H\left( {1,2} \right)} & {H\left( {1,3} \right)} \\\vdots & \vdots & \vdots \\{H\left( {N,1} \right)} & {H\left( {N,2} \right)} & {H\left( {N,3} \right)}\end{bmatrix}},{and}} & {{Eq}.\mspace{14mu} 15} \\{P = {{{trans}\begin{bmatrix}{Bs} & {Ba} & {Be}\end{bmatrix}}.}} & {{Eq}.\mspace{14mu} 16}\end{matrix}$

Then the estimate of P (EP) is made using Eq. 17, where

EP=inv[trans[H]*H]*trans[H]*D1  Eq. 17,

where inv[ ] is the matrix inversion operation.

For the Eq. 10, a least squares problem leading to a batch solutioncould take the form of Eq. 18, where

$\begin{matrix}{\begin{bmatrix}\begin{matrix}{{{{dRm}(1)}/{{Um}(1)}} + {{\cos \left\lbrack {{Am}(1)} \right\rbrack}*{\cos \left\lbrack {{Em}(1)} \right\rbrack}}} \\\vdots\end{matrix} \\{{{{dRm}(N)}/{{Um}(N)}} + {{\cos \left\lbrack {{Am}(N)} \right\rbrack}*{\cos \left\lbrack {{Em}(N)} \right\rbrack}}}\end{bmatrix} = {\quad{\begin{bmatrix}{F\left( {1,1} \right)} & {F\left( {1,2} \right)} & {F\left( {1,3} \right)} \\\vdots & \vdots & \vdots \\{F\left( {N,1} \right)} & {F\left( {N,2} \right)} & {F\left( {N,3} \right)}\end{bmatrix}\begin{bmatrix}{Bs} \\{Ba} \\{Be}\end{bmatrix}}}} & {{Eq}.\mspace{14mu} 18}\end{matrix}$

Similar to Eq. 13, a way to solve Eq. 18 as a least squares problem isto rewrite it in the form

$\begin{matrix}{{{D\; 2} = {F*P}},{where}} & {{Eq}.\mspace{14mu} 19} \\{{{D\; 2} = \begin{bmatrix}\begin{matrix}{{{{dRm}(1)}/{{Um}(1)}} + {{\cos \left\lbrack {{Am}(1)} \right\rbrack}*{\cos \left\lbrack {{Em}(1)} \right\rbrack}}} \\\vdots\end{matrix} \\{{{{dRm}(N)}/{{Um}(N)}} + {{\cos \left\lbrack {{Am}(N)} \right\rbrack}*{\cos \left\lbrack {{Em}(N)} \right\rbrack}}}\end{bmatrix}},} & {{Eq}.\mspace{14mu} 20} \\{{F = \begin{bmatrix}{F\left( {1,1} \right)} & {F\left( {1,2} \right)} & {F\left( {1,3} \right)} \\\vdots & \vdots & \vdots \\{F\left( {N,1} \right)} & {F\left( {N,2} \right)} & {F\left( {N,3} \right)}\end{bmatrix}},{and}} & {{Eq}.\mspace{14mu} 21} \\{P = {{{trans}\begin{bmatrix}{Bs} & {Ba} & {Be}\end{bmatrix}}.}} & {{Eq}.\mspace{14mu} 22}\end{matrix}$

Then the estimate of P (EP) is provided in Eq. 23, where

EP=inv[trans[F]*F]*trans[F]*D2  Eq. 23.

A method of solving Eq. 5 may include the steps of:

-   -   a) collect radar measurements dRm(i), Am(i) and Em(i) for i=1, .        . . N, N≧3;    -   b) collect host module outputs Sm(i) and Ys(i) for i=1, . . . N;    -   c) determine the host velocity components Um(i) and Vm(i) using        Um=Sm*cos [Ys], and Vm=Sm*sin [Ys], where if the host-vehicle 12        is going straight the substitution may be simplified by using        Um(i)=Sm(i) and Vm(i)=0; and    -   d) determine the estimate of P (EP) using Eqs. 13-17.

In another embodiment of the algorithm 18, a batch solution shown aboveis solved at each time instant using detections from only that timeinstant. This requires a test at each time instant which ensures thatthe least squares problem is sufficiently well-conditioned for asolution to be attempted. A simple form of this test requires a minimumnumber of detections having sufficient diversity in the detected ormeasured azimuth and elevation angles. The single-time-instant estimatesfor Bs, Ba, and Be are then used to drive low-pass filters producingslowly time-varying estimates of these parameters. This implementationhas the benefit of relative simplicity, but has the drawback that itdiscards valid detection data at time instants where there areinadequate detections for solving the single-time-instant problem.

The algorithm 18 can also be implemented as a recursive least squares orKalman filter. Implementations having windowed intervals of interest orfading memory over longer intervals are possible. A practitioner skilledin the art could easily envision how to formulate such a filter based onthe Main Equation (Eq. 5) or the Simplified Equation (Eq. 10) shownabove.

The algorithm 18 uses raw or measured radar detections of themeasured-range-rate 22, the measured-azimuth-angle 24, and themeasured-elevation-angle to targets (i.e. the objects) which areperceived to be stationary. The determination that a target or object isstationary relies on the speed signal from the host-vehicle, which isassumed to be corrupted by the speed-scaling-error 36. It also relies onthe measured angles, which are assumed to have bias errors due to themisalignment. Fortunately, the determination of stationary/moving isrelatively insensitive to the assumed small alignment errors. However,it has been observed that the same is not true of thespeed-scaling-error as stationary targets have been determined by thetracker to be moving targets when the speed of the host-vehicle isrelatively high, greater than 100 kph for example. Therefore, it isrecognized that it is preferable that the auto-alignment is performed ata not too great amount of speed, less than 60 kph for example. At lowerspeeds the magnitude of the vehicle speed-scaling-error is small enoughfor the stationary targets to be correctly classified as stationary, orthat the stationary/moving threshold is increased with increasingvehicle speed in a way that accounts for the maximum anticipated levelof speed-scaling-error. The auto-alignment algorithm is most accuratewhen run under conditions where the lateral and vertical components ofrelative-to-Earth velocity of the radar-sensor are nearly zero. Thus,ideal conditions are a straight trajectory on smooth asphalt.

Estimation problems such as the one described in this document rely onan observability condition for success. The parameters are observable ifand only if there is sufficient information in the observed quantitiesfor the parameters to be uniquely identified. In the batch formulationof the present algorithm, observability is related to the rank of the(noise-error-free version of the) Nx3 matrix (i.e., it needs to be 3).It has been found that the observability condition is satisfied if thereare at least three detections having sufficient azimuth and elevationangle diversity. The auto-alignment algorithm described herein ispresented under an assumption of a sufficiently rich and diverse set ofdetections that the parameters are observable.

The implementations of the algorithm described herein require estimatesof the three Cartesian components of the relative-to-Earth velocity ofthe radar-sensor, Um, Vm, Wm. Though a measured vehicle speed signal isassumed to be available (possibly corrupted by the speed-scaling-error),the measurement/estimation of these three quantities requires some sortof model of the vehicle dynamics, and other sensors such as yaw-ratesensor, pitch-rate sensor, steering wheel sensor, etc. Well knownalgorithms are available for this subject.

The algorithm 18 described herein is most useful if it includes aconfidence indication, in addition to the miss-alignment estimates. Thisconfidence indicator signals to the consumer of the miss-alignmentestimates whether or not they are ready to be used and trusted. Thealgorithm generally will start out by providing somewhat erroneousestimates of the desired quantities, but the error in the estimatesshould rapidly decrease to a steady-state level. Once this steady-statelevel is achieved, the algorithm should signal high confidence in theestimates. If something goes wrong and the estimates don't appear to beconverging to useful values, then a low confidence should be signaled.Low confidence should also be signaled during the initial transientperiod prior to successful convergence.

Two schemes for identifying a condition of convergence or highconfidence are now described. In one scheme, both short-term andlong-term averages are computed for the estimated bias values. If theseagree, then successful convergence is indicated. In another scheme, therange-rate residual error (i.e. the difference between the predictedrange-rate and the measured range-rate of those stationary objects) ismonitored. Ideally, a short-term average of these range-rate residualerrors will converge to a minimum value, and when this value is achievedthen successful convergence is indicated.

The algorithm 18 has been tested using simulated data in which theactual error parameter values are known, and using real sensor data inwhich the actual error parameters are not known.

FIG. 4 shows the results of 60 simulation runs, each representing adifferent level of actual simulated azimuth angle bias between −3.0 and+3.0 degrees. In each simulation run, the simulated speed-scaling-erroris 5.0%, the simulated elevation angle bias is 2.0 degrees, and thesimulated range rate has a bias of −0.1 meters/second. The simulatedmeasurements of both azimuth and elevation angles and range rate areadditionally corrupted by zero-mean Gaussian noise having standarddeviations of 1.0 degrees (azimuth), 2.0 degrees (elevation), and 0.1meters/second (range rate). For each simulation run at a particularazimuth angle bias level, sufficient data points are simulated to allowthe algorithm estimates to converge. The actual or true azimuth anglebias varies from −3.0 to +3.0 degrees and the estimated azimuth bias isproduced by the algorithm 18. In this plot, the horizontal axis labeled“simulation index” represents different simulation runs, each having aparticular value of simulated azimuth angle bias as given by thecorresponding value of the actual azimuth bias.

FIGS. 5-7 show estimates of azimuth angle bias, elevation angle bias,and speed-scaling-error, respectively, which were obtained for a singledata file from an exemplary radar sensor. In these plots, the horizontalaxis labeled “simulation index” represents Time (expressed in number ofradar scans). Since this is real sensor data, the actual or true valuesof the error parameters are not known. The plots show reasonable-lookingconvergence to values in the expected ranges.

FIG. 8 shows that an estimation quality measure is significantlyimproved by the obtained estimates, compared to initial assumed valuesof zero for all of the error parameters being estimated. Specifically,the residual error (which is the disagreement between themeasured-range-rate and a predicted-range-rate) is smaller after theerror parameters are compensated.

Accordingly, a radar system (the system 10), a controller 34 for thesystem 10, and a method of operating the system 10 is provided thatauto-aligns a radar-sensor 14 on a host-vehicle 12 by simultaneously(i.e. not separately or sequentially) solves for errors in ameasured-range-rate (dRm), a measured-azimuth-angle (Am), and ameasured-elevation-angle (Em), while the host-vehicle 12 is moving. Anestimation scheme in which the quantities of interest are jointlyestimated is generally superior to alternative methods, due to thesimultaneous accounting for all of the error sources. Good estimates ofthe error parameters estimated by the algorithm 18 are of criticalimportance to tracking and fusion systems using the radar-sensor, asthey allow the important quantities host speed, azimuth angle andelevation angle to be compensated for the errors present there.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A radar system with auto-alignment suitable for use in anautomated vehicle, said system comprising: a radar-sensor used to detectobjects present in a field-of-view proximate to a host-vehicle on whichthe radar-sensor is mounted, said radar-sensor operable to determine ameasured-range-rate (dRm), a measured-azimuth-angle (Am), and ameasured-elevation-angle (Em) to each of at least three objects presentin the field-of-view; a speed-sensor used to determine a measured-speed(Sm) of the host-vehicle; and a controller in communication with theradar-sensor and the speed-sensor, said controller configured tosimultaneously determine a speed-scaling-error (Bs) of themeasured-speed, an azimuth-misalignment (Ba) of the radar-sensor, and anelevation-misalignment (Be) of the radar-sensor based on themeasured-range-rate, the measured-azimuth-angle, and themeasured-elevation-angle to each of the at least three objects, whilethe host-vehicle is moving.
 2. The system in accordance with claim 1,wherein, said controller further configured to determine an actual-speed(Sa) based on the measured-speed and the speed-scaling-error, anactual-azimuth-angle (Aa) to the objects based on theazimuth-misalignment and the measured-azimuth-angle, and anactual-elevation-angle (Ea) to the objects based on theelevation-misalignment and the measured-elevation-angle.
 3. The systemin accordance with claim 1, wherein each of the at least three objectsis characterized as stationary.
 4. The system in accordance with claim1, wherein the system includes a yaw-rate-sensor used to determine ayaw-rate of the host-vehicle, wherein the controller is furtherconfigured to determine a side-slip-angle (Ys) of the host-vehicle basedon the yaw-rate, and further determine the speed-scaling-error, theazimuth-misalignment, and the elevation-misalignment based on theside-slip-angle.